Alexandrite
“Emerald by day, ruby by night,”
Alexandrite is well known for displaying one of the most remarkable color changes in the gem world — green in sunlight and red in incandescent light. Originally discovered in Russia’s Ural Mountains in the 1830s, it’s now found in Sri Lanka, East Africa and Brazil, but fine material is exceptionally rare and valuable. Alexandrite results from small scale replacement of aluminum by chromium ions in the crystal structure, which causes intense absorption of light over a narrow range of wavelengths in the yellow region (520-620 nm) of the visible light spectrum. Because human vision is most sensitive to green light and least sensitive to red light, alexandrite appears greenish in daylight where the full spectrum of visible light is present, and reddish in incandescent light which emits less green and blue light.
Alexandrite |
|
Variety of |
Chrysoberyl |
Crystallography |
Orthorhombic |
Colors |
Varies in color with incident light: green, blue-green, or pale green in daylight; mauve, violet to red, purplish in incandescent light. |
Luster |
Vitreous |
Hardness |
8.5 |
Birthstone |
June |
Etymology |
Named after Czar Alexander II of Russia. |
Origins |
Ural Mountain, Brazil, Sri Lanka, Burma, Madagascar, Tanzania. |
Formula |
BeAl2O4 + Cr |